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Author Topic: Trimming out a P30?  (Read 2758 times)
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flytime
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« on: April 24, 2014, 08:04:19 PM »

Hi, folks, just got back into this fine hobby after around 15 years away from it. I used to fly P30s in my youth so I'm starting off again by building a One Nite 28.
I would appreciate any advice on how to trim out my finished P30. Also when building, should I build in any down/side thrust, washout etc? I would also like to build some Wakefields too. Would trimming these be similar to a P30?
 
Cheers

Nick
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HoveToo
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« Reply #1 on: April 25, 2014, 04:50:05 AM »

As a old newbie I flew my first build - a ON28 last night. I built per the plan which has plenty of downthrust and at my stage of knowledge I will carry on doing this because I found that in my builds there are many twists and turns in the completed plane  that it has to be flown first before attempting any trimming. Mine did many test glides without the prop and motor, firstly because that was the advice that I'd read and secondly because the prop and motor were still in my garage. Anyway, it floats beautifully and returned to base in the right number of pieces.

The only change I made was to add some thin ply strips to mount the stab and rudder assembly on and I added an aluminium tab to the rudder. I think I will add another to the right hand side wing to make sure it turns right as it is a bit straight at the moment.
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DaddyO
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« Reply #2 on: April 25, 2014, 11:53:07 AM »

Depends on your motor size/ how hard you wind 'em Nick. A cruising P30 on 6 x 3/32 is a farly genteel beastie.  Cheesy

If you wind it hard you'll find you need a fair bit of downthrust (at least that's what I've usually found) Mine usually use @ 5 down and 3 right with some tail tilt (right side up) and a bit of differential warp (ie washin on right inner with both tips washed out the same or left hand tip washed out about 5mm) I usually find a small gurney strip on the fin or a tab is needed too, but don't use ali for these because it's too heavy and can be bent out of position accidentally.

Good luck with 'em
Paul

ps
Wakes are a different kettle of fish; old uns have a lot of torque when fully wound so take small steps unless you like re-builds. Tongue Others are in a better position to advise on the newer ones
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Starduster
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« Reply #3 on: April 25, 2014, 01:19:17 PM »

I copied this from a post on this website a while ago, but I can't find the original post, so I'm just going to paste the information here. I am not the original author. These are instructions on how to trim a old-school Wakefield (No auto-surfaces) I am following these directions in order to trim my Bob White No. 22:

"I mentioned to Derek that I'd add some comments on trimming locked down F1B models for high performance.

In my opinion getting a very high performance from a locked down model is much harder than getting high performance from a similar model with full auto-surfaces. At first blush it might seem non-intuitive that a simple locked down model would be harder to trim, but in practice this is the case. You see, with a locked down model, every change to the declage, warps, CG or thrust-line has multiple effects that must be accounted for. For example, if the plane fails to turn correctly in the cruise, you can simply add some additional right thrust. But this can cause problems in the burst if you over do it. You could then add some left rudder to straighten the burst, but then you'd open up the cruise again, and possibly make the glide too tight. And so on... You can end up chasing your tail trying to get a good all around trim. With auto-surfaces you can separate the burst/cruise/glide and trim them independently.

This is where the P.G.I. trim comes in. This trim is the genius of Jean Wantzenreither (France) who developed this method of trimming a locked-down duration rubber model over many years.
For reference, P.G.I. is an acronym for: P = Piqueur (french for the thrust line which should pass through the vertical C of G), G = Gravite' (the C of G should be as far back as practical), and I = Incidence (the wing should have a negative incidence with respect to the fuselage centerline). There is an excellent book available from FFQ that covers many of Jean's articles that outlines his thinking. http://www.freeflightquarterly.com/ffqcurrent.html

The key parts to the concept is that to reduce the looping effect of the high speed burst, you need to reduce the declage as much as possible. So the burst determines the maximum amount of declage that you can carry. To reduce the looping effect from the thrust line, you place the thrust line so that it passes through the vertical C of G. This works best if the nose moment arm is long and the pylon or wing saddle is very low.
Normally, if you reduce the declage and add a large amount of what appears to be down thrust you'd have an airplane that will not climb in the cruise.
To make the plane climb at a nose up angle in the cruise you need to do two things:

1) reduce the wing's angle of attack relative to the fuselage centerline. My No 23 used on average -2.0 degrees of negative incidence on the ing and -4.5 degrees of down thrust. Thus the actual down thrust relative to the wing is 2.5 degrees. More negative on the wing can reduce the effective down thrust and help the plane climb more nose up.

2) reduce the stabilizer's aspect ratio. This is very clever imo and one of Jean's best ideas. Reducing the stab's aspect ratio has a big effect on the stabilizer's lift slope (rate of change of lift versus angle of attack or C/L vs Alpha). The lower the aspect ratio the lower the lift slope. This means that at high speeds the stab is very effective (and thus can do it's job of holding the nose down in the burst), but at lower speeds, the low lift slope helps make the stab less effective and will keep the plane's nose up in the cruise.

So some elements that can be used to trim a locked down F1B for maximum performance are:

PGI trim:
-CG far back (No 23 is 75%)
-wing set at negative angle
-wing mounted on low pylon or saddle type mount
-long nose
-low aspect ratio stabilizer
-large amounts of dihedral
-minimum size fin mounted as far aft as possible

To achieve each of these elements I made sure to make as many parts of the model adjustable for trimming as I could. Thus the thrust-line was adjustable with small set screws. The prop pitch could be easily adjusted with a nut on each blade. The pylon was strapped to the fuselage using a high strength tape so that it could be moved fore or aft to set the final CG. The wing incidence could easily be adjusted with screws on the pylon. The individual wing halves could be set to the desired differential wing twist using a set screw. The fin angle was screw adjustable. The stab incidence was screw adjustable as was the stab tilt. The wing wire could be easily bent to add or remove wing dihedral.

This sounds complicated, but in practice I could trim a model quite quickly using these adjustments and often could set up a model on the bench (using the previous model as reference) and be very close to final trim on the first flights.

The basic trim procedure was as follows:
-set the CG as per the plan (75% for my models)
-set the declage to 2 degrees and the wing at -2 degrees
-set a small amount of left rudder offset and a small amount of left stab tilt
-set about 1/16" of left wing wash-out
-set about 2 degrees of right thrust and 4.5 degrees of down to start

I didn't bother with test glides as I find they don't tell me too much.
I start with 200 to 220 turns and launch smoothly just to the right of the wind at about a 30 degree angle upwards at first. I watch the climb and see if it is turning smoothly to the right (but not too tight) and then watch the glide after the prop folds.
If this looks o.k., I immediately increase the power to about 80% of max. If not I make some adjustments until the low power test looks safe.
At 80% power (by torque, not turns) I launch much steeper (60 to 70 degrees up) I watch the initial climb to see if it is straight and if the plane wants to kook to the right. A right hook is usually caused by excess declage and/or insufficient left rudder offset. I reduce declage and tweak a bit of left rudder until the initial climb is fairly straight out with a slight right hand bias, that transitions into a smooth, open right hand spiral. The glide is trimmed with CG changes and differential wing tip weight (my left tip was always slightly heavier than the right). The thermal behavior is trimmed with the wing twist. If the plane wants to spin-in in strong lift then some wash-out is removed from the left wing. If it fails to tighten in lift then wash-out is added to the left wing.
The right thrust and left rudder adjustment is carefully balanced to achieve a straight initial burst and a positive but open spiral in the cruise.

When developing the model the fin size had to be adjusted down several times before it was found to be too small (shown by slight dutch roll in the glide). Too large and the plane will hook to the right in the burst. A good idea was to make the prototype fin top from sheet balsa so that it could be trimmed away as needed.
Also, I had to make several stabs with different airfoils or planforms to get the climb I was after.

While achieving a near perfect trim compromise is possible, it does take time and effort. The reward for me was that the airplane was very competitive in it's day even with the full auto-surface models, and was extremely simple to fly. I used a fuse DT and would just wind the plane and throw it. No timers to set, nothing to check and nothing to go wrong. Very simple to fly on the field. Very tricky to get to that point."


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HoveToo
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« Reply #4 on: April 27, 2014, 07:15:48 AM »

Daddyo and Iceman - thanks for this advice. When the weather behaves I will give it a try. But first I need to build some stable trimming devices and appropriate warps, at least the weather is right for that bit...

Ian
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Modelace
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« Reply #5 on: April 30, 2014, 10:53:24 AM »

I suggest 3 degrees down and right, C/G at 30%, equal washout both wings (1/8"). Test glide with prop in place..no power until glide is straight ahead, gentle slope to a soft landing.
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billdennis747
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« Reply #6 on: October 21, 2014, 08:44:12 AM »

I am just finishing a Teacher's Pet P30. What surprised me is the 95% CG.  I haven't used a cg that far back since I was making holes in the ground with slow open power models. What is the reasoning behind this?
Bill
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« Reply #7 on: October 21, 2014, 08:48:39 AM »

I suggest 3 degrees down and right, C/G at 30%, equal washout both wings (1/8").

CG at 30%? Seriously? Roll Eyes

I am just finishing a Teacher's Pet P30. What surprised me is the 95% CG.  I haven't used a cg that far back since I was making holes in the ground with slow open power models. What is the reasoning behind this?

CG is set based on tail volume. More tail volume => optimum CG is further aft. Tail volume is proportional to tail moment and stab area. Teacher's Pet has a lot of both.
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billdennis747
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« Reply #8 on: October 21, 2014, 08:54:41 AM »

Quote
CG is set based on tail volume. More tail volume => optimum CG is further aft. Tail volume is proportional to tail moment and stab area. Teacher's Pet has a lot of both.

Thanks. So what is the advantage of this setup? I have noticed that modern P30s have the wing much further back and presumably more forward CG.
« Last Edit: March 16, 2019, 03:45:15 PM by Ratz » Logged
PeeTee
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« Reply #9 on: October 21, 2014, 09:51:37 AM »

Bill

Paul is a long time Teachers Pet flyer, and pretty successful with it too. If he reads this, perhaps he'll provide you with details of his set up.

I suspect that part of the more rearward wing position is because of the use of 4x 1/8" motors running the length of the fuselage.  I think my models have a CofG around 60-65% and I'm now using 6 strands of 3/32"

Peter
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« Reply #10 on: October 21, 2014, 10:13:38 AM »

I suspect that part of the more rearward wing position is because of the use of 4x 1/8" motors running the length of the fuselage.  I think my models have a CofG around 60-65% and I'm now using 6 strands of 3/32"

It would look to be a combination of smaller stabs, and the motor's CG being further aft due to the longer motors being run all the way to the back. This requires moving the wing back, which in turn reduces tail volume and moves the % chord optimum CG forward.
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billdennis747
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« Reply #11 on: October 21, 2014, 10:22:42 AM »

I suspect that part of the more rearward wing position is because of the use of 4x 1/8" motors running the length of the fuselage.  I think my models have a CofG around 60-65% and I'm now using 6 strands of 3/32"

It would look to be a combination of smaller stabs, and the motor's CG being further aft due to the longer motors being run all the way to the back. This requires moving the wing back, which in turn reduces tail volume and moves the % chord optimum CG forward.
Thanks all. I still don't understand the benefit of the rearward CG setup. I would have thought it would be more prone to poor stall recovery?
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« Reply #12 on: October 21, 2014, 11:20:01 AM »

Ask JO'D the next time you see him!
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billdennis747
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« Reply #13 on: October 21, 2014, 12:30:18 PM »

Ask JO'D the next time you see him!
I'm always on the phone to him and should have asked last night. I need to write a list of questions!
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Dave Andreski
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« Reply #14 on: October 25, 2014, 12:22:30 PM »

I'm always on the phone to him and should have asked last night. I need to write a list of questions!

Yes,
Please do!
While you're at it ask him if he has any construction pics of the updated, geodetic wing construction using the thinner, Davis/Davies? airfoil as suggested in FreeFlight News, January, 2006.

Did he continue to use the 'tip up stab' DT after he updated the plan?

Thanks,

Dave
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« Last Edit: March 16, 2019, 03:47:27 PM by Ratz » Logged

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billdennis747
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« Reply #15 on: October 25, 2014, 06:26:02 PM »

I'm always on the phone to him and should have asked last night. I need to write a list of questions!

Yes,
Please do!
While you're at it ask him if he has any construction pics of the updated, geodetic wing construction using the thinner, Davis/Davies? airfoil as suggested in FreeFlight News, January, 2006.

Did he continue to use the 'tip up stab' DT after he updated the plan?

Thanks,

Dave

Dave, no he just said he has no constructional shots but may detail it in one of his future Aeromodeller articles. I forgot to ask about the DT but I have never seen him with anything other than a pop up tailplane
« Last Edit: March 16, 2019, 03:48:25 PM by Ratz » Logged
Dave Andreski
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« Reply #16 on: October 25, 2014, 08:14:53 PM »

Thanks Bill.
I'm sure the 'Pet' is quite good when built to the original plan but seems a little difficult for me at the present time.
I'll have to give the plan a thorough study before commiting.

Your Teachers Pet looks Great!

Dave
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billdennis747
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« Reply #17 on: October 26, 2014, 03:33:08 AM »

Thanks Bill.
I'm sure the 'Pet' is quite good when built to the original plan but seems a little difficult for me at the present time.
I'll have to give the plan a thorough study before commiting.

Your Teachers Pet looks Great!

Dave
Dave, it's quite straightforward but I still struggle with the weight. I think the covering did me in and I am going to have to get to grips with mylar
Bill
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« Reply #18 on: October 26, 2014, 05:05:25 AM »

Morning Bill sorry for my tardy response, but I just spotted this thread  Roll Eyes

Anyway with regard the rearward CofG set up I started mine off as shown on the plan with the 95% CofG (was it really all that way back?) One of the reasons for the set up by the way is to help prevent the horrible loop on launch that you can get with a powerful (!) motor. Rearward balance requires less incidence difference between wing and tail to get a nice glide and the lower incidence helps prevent the loop (Sorry if any aerodynamic types are offended by my simplistic reasoning) I found that pushing the CofG forward improved it and flew it at 55% for a while before moving it back again to 60-70% which is a good figure IMO

Anyway with regard set up here's my note's for the original one as flown in it first couple of seasons (Weights are as originally built, but climbed after a bit of flying) -

Fuz 20gms, Wing 15gms, Prop/noseblock 10gms, tail 6gms.
Wing warps - left tip -5mm washout, right tip -1mm washout, both inner panels flat
5/64 right thrust and 5/64 down thrust
3/32 under tail trailing edge + 1/32 right tail tilt
20 x 10mm tab on fin 20 degrees to right
Flew R/R with a prop run of @ 40 seconds

That should hopefully get you somewhere near if you set up the incidence first and then move the balance to get the glide (Sorry, but because I kept fiddling with the balance I haven't got the setting I ended up with - probably 60% or so looking at the incidences above) Incidentally this model never placed lower than third in any competition it flew in, which is why I have stuck with the design.

These days I fly a version of the updated TP which I believe you have the notes for? I use 6 x 3/32 in a fairly light airframe (43gms) Mylar and tissue on fuz, lt jap only on wing, mylar tail. My second one has a mylar all over and has taken a long time to get flying well with lots of little tweaks to wing leading edge shape and turbulators - it now goes okay, but doesn't climb as high as the tissue wing version; still good enough for comps though.

There - apologies for the long winded response, but I hope it helps. Feel free to come over and take a look if we are on the field together at any time

Cheer for now
Paul

ps - Did you go over to Nth Luff yesterday (I was putting some graphics on a van, so missed out)  Sad
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« Reply #19 on: October 26, 2014, 05:48:17 AM »

Paul
Yes I was there enjoying myself in Coupe with my Baron Knight and didn't come last again. Must set my sights higher. You will have to introduce yourself because while I recognise faces, names, and noms de plume, are a problem.
Thanks for all those hints. So with 95% cg it sounds like SLOP trim! I'm not sure what to do now because I just finished the thing and of course I can't alter the cg without ballast. I want to fly it in the experimental meeting but will only have three days to trim (off to the beach again) so it might be chuck it and see.
Bill
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« Reply #20 on: October 26, 2014, 08:33:45 AM »

No sweat Bill (I'm Paul Seeley by the way) I'm also hoping to get to the experimental meet too, so may see you there assuming the weather is reasonable.

By way of encouragement mine flew off the board with the trim as shown on the plan apart from extra down and side when I started using more turns; in fact it was my first freeflight model and I can well recall almost losing it on it's first outing on about 150 turns at Wyken Common (in Coventry). I did a few hand glides and then put some turns on and stood on the small hillock by the church and waited for what I thought was lift . . . the model climbed away nicely to about 70' and showed little signs of descending till the fuse DT kicked in and plonked it on top of a bramble bush about a minute later Tongue (The model emerged unscathed - I was just wearing shorts and T shirt so fared slightly worse)

In short this was the model that got me hooked on Freeflight (Has a lot to answer for!)

Cheers for now
Paul
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« Reply #21 on: October 26, 2014, 08:52:27 AM »

OK Paul. I'll see what happens! I had no idea P30 was so involved.
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« Reply #22 on: October 28, 2014, 06:23:02 PM »

Bill and Paul,
Thanks for the info.
Much appreciated.
Dave
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« Reply #23 on: November 09, 2014, 01:48:40 PM »

I went to the meeting at Luffenham today with the untried Teacher's Pet. I quickly sorted out the glide and then two trimming flights on 700 and 1200 turns, then three maxes in the comp and into a three way flyoff! I was using 6 strands of 3/32 but stripped from some oldish 1/4 that I suspect was sport. The first three motors were fine; the flyoff one just got it above head height, where it stayed for 1:17.
However I was very pleased. PeeTee has kindly given me one of these orange props and at some point I will build another, which will weigh closer to 40g than 52g.
Thanks all for the advice.
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« Reply #24 on: November 09, 2014, 01:55:27 PM »

Nice one Bill - sorry I couldn't get up there myself.
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